Microplasma devices developed by the present inventors have been formed in various materials and configurations. Such devices are capable of igniting and sustaining glow discharges in microcavities having a characteristic dimension between approximately 5 μm and 500 μm. Electrodes are generally designed to ignite a plasma within each microcavity. Designs for the electrodes differ but most are azimuthally symmetric with respect to one or all cavity apertures. Prior arrays developed by the present inventors and colleagues have many applications, such as displays, lighting, as well as the production of ozone for water treatment.
For example, Park et al, U.S. Published Application Number 20100296978 discloses microchannel lasers having a microplasma gain medium. In that application, microplasma acts as a gain medium with the electrodes sustaining the plasma in the microchannel. Reflectors can be used in conjunction with the microchannel for obtaining optical feedback and lasing in the microplasma medium in devices of the invention for a wide range of atomic and molecular species. Several atomic and molecular gain media will produce sufficiently high gain coefficients that reflectors (mirrors) are not necessary. FIG. 4 of that application also discloses a microchemical reactor that is suitable for air purification and ozone production because of the channel lengths and large plasma power loadings (watts deposited per unit volume) that are available. However, fabrication costs associated with channels of extended length present an obstacle to commercialization for this technology for many applications that would benefit from ozone production.
Ozone is the strongest oxidant and disinfectant available commercially. Mechanisms of disinfection using ozone include direct oxidation/destruction of bacterial cell walls, reactions with radical by-products of ozone decomposition, and damage to the constituents of nucleic acids. Presently available commercial devices for the large scale production of ozone are generally expensive devices having high power requirements. Ozone is produced when oxygen (O2) molecules are dissociated by an energy source into oxygen atoms. Collisions with oxygen molecules produce ozone (O3), which must be generated at the point of treatment because the lifetime of O3 in air at atmospheric pressure is in the order of minutes. Commercial ozone generators having sufficient capacity for municipal water treatment, for example, are large (as much as 10-15 ft. in length) and have demanding power requirements (150-200 kVA). Furthermore, the conversion of feedstock gases into O3 is typically inefficient. Existing commercial processes for producing O3 in large volume typically convert 15%-18% of the oxygen (O2) feedstock gas into O3. Maintenance of such system is also problematic owing to a large number of ceramic parts and fouling of device components by nitric acid. Inexpensive and compact devices for high-efficiency generation of ozone would have many important applications.